Potassium
' Potassium' is the chemical element with the symbol K atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash. Elemental potassium is a soft silvery-white metallic alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the evolved hydrogen. Potassium ion is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations in plant cells, and in a mixed diet, it is most highly concentrated in fruits. Potassium and sodium are chemically similar, since both are alkali metals. However, their functions in organisms are quite different, especially in animal Characteristics Potassium is the second least dense metal; only lithium is less dense. It is a soft, low-melting solid that can easily be cut with a knife. Freshly cut potassium is silvery in appearance, but in air it begins to tarnish toward grey immediately. In a flame test, potassium and its compounds emit a lilac color, which may be masked by the strong yellow emission of sodium if it is also present. Cobalt glass can be used to filter out the yellow sodium color. Potassium concentration in solution is commonly determined by flame photometry, atomic absorption spectrophotometry, inductively coupled plasma, or ion selective electrodes. Potassium hydroxide reacts strongly with carbon dioxide to produce potassium carbonate, and is used to remove traces of CO2 from air. Potassium compounds generally have excellent water solubility, due to the high hydration energy of the K+ ion. The potassium ion is colorless in water. Methods of separating potassium by precipitation, sometimes used for gravimetric analysis, include the use of sodium tetraphenylborate, hexachloroplatinic acid, and sodium cobaltinitrite Potassium reacts very violently with water producing potassium hydroxide (KOH) and hydrogen gas. This reaction is exothermic and temperature produced is sufficient to ignite the resulting hydrogen. It in turn may explode in the presence of oxygen. Potassium hydroxide is a strong alkali which causes skin burns. Finely divided potassium will ignite in air at room temperature. The bulk metal will ignite in air if heated. The water also produces potentially explosive hydrogen gas. Potassium reacts violently in the presence of halogens and will detonate in the presence of bromine. It also reacts explosively with sulfuric acid. During combustion potassium forms peroxides and superoxides. These peroxides may react violently with organics present such as oils. Both peroxides and superoxides may react explosively with metallic potassium. Since potassium reacts with water vapour present in the air, it is usually stored under anhydrous mineral oil or kerosene. Unlike lithium and sodium, however, potassium should not be stored under oil indefinitely. If stored longer than 6 months to a year, dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, which can detonate upon opening. It is recommended that potassium not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum. Due to the highly reactive nature of potassium metal, it must be handled with great care, with full skin and eye protection being used and preferably an explosive resistant barrier between the user and the potassium. Value The base value of each unit of ranges between 5 and 10Ð per unit, with up to 3 units being found at any one time. Presence on Mars: Common Category:Chemical elements